Thin film perpendicular magnetic recording head, their fabrication process and magnetic disk drive using it

ABSTRACT

Thin film perpendicular magnetic head with a narrow main pole capable of a high recording density in excess of 100 gigabits per square inch and generating a high magnetic recording field, while also being modified to suppress remanent magnetic fields occurring immediately after writing operation. A return path is provided for supplying a magnetic flux to the main pole, and an conductive coil for excitation of the main pole and return path. The main pole has a pole width of 200 nanometers or less, and a magnetic multilayer made up of a high saturation flux density layer and low saturation flux density layer. The low saturation flux density layer and the high saturation flux density suppress remanent magnetization and prevent erasing after writing by utilizing a closed magnetic domain structure in the pole.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation application of application Ser. No.11/802,297, filed May 22, 2007, now U.S. Pat. No. 7,532,433, which iscontinuation of U.S. patent application Ser. No. 10/644,022, now U.S.Pat. No. 7,221,538, filed Aug. 20, 2003, which claims priority fromJapanese patent applications JP 2003-196859, filed on Jul. 15, 2003, andJP 2003-012988, filed on Jan. 22, 2003, the contents of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film perpendicular magneticrecording head, their magnetic head fabrication process and magneticdisk drive for a highly reliable magnetic head with stable operationcapable of generating a high magnetic recording field even on narrowtracks for high density magnetic recording.

2. Description of Related Art

In recent years, digitalization of diverse media has been making rapidprogress along with advancements in information processing technology.Besides personal computers and servers, home appliance and audio devicesmust store huge amounts of digital information, creating an increasingdemand greater than ever before for large capacity magnetic disk drivesforming the core of non-volatile file systems. Large capacity diskdrives in other words signifies recording on a medium with a higher bitdensity or in other words, a higher areal recording density.

A method called longitudinal magnetic recording is the generally usedmethod for actual recording on magnetic disk drives. The longitudinalmagnetic recording utilizes as a recording medium, a ferromagnetic layerpossessing large magnetic coercivity in a direction parallel to the disksubstrate surface, and records information by magnetizing the recordingmedium along the substrate area surface. In this case, an inversemagnetized section formed to face the longitudinal magnetization at a180 degree angle is the bit 1.

In order to increase the longitudinal recording density, both the bitdensity towards the disk periphery (linear recording density) and thebit density radially along the disk (track density) must besimultaneously increased. Increases in the track density are limited bythe pole width forming process for the read/write head and by themechanism for positioning accuracy. However these factors are nothingmore than technical issues. Increases in the linear recording densityhowever are subject to basic restrictions due to the fact that therecording medium is an aggregate of ferromagnetic particles.

In the longitudinal magnetic recording method, magnetized sections thatmutually oppose one another are mainly magnetic reversals. Near thesemagnetic reversals, large internal magnetic fields calleddemagnetization fields occur in a direction diminishing themagnetization. Transition areas or in other words, areas not having ahigh enough magnetic value are formed in a finite width in thesemagnetic reversals by the demagnetization fields.

Problems such as shifts in the actual position of the magnetic reversaloccur when adjoining magnetic transition areas interfere with each otherin locations when the bit length is short. These problems make itnecessary to reduce the magnetic transition areas to at least a sizesmaller than the bit length. Increasing the linear recording densitytherefore requires a property on the medium where magnetizationovercomes the demagnetization field. More specifically, along withimproving the magnetic coercivity of the medium, the thickness of themagnetic recording layer must be reduced to suppress the demagnetizationfield.

The linear recording density is therefore greatly restricted by themagnetic properties and structure of the medium.

In the standard longitudinal recording, the ratio of linear recordingdensity to track density is preferably about 5 to 10 times. To attain arecording density of 100 gigabits per square inch (10¹¹ bits per squareinch) based on this condition, the bit length towards should be madeabout 25 nanometers in the peripheral direction of the disk. However,estimating the properties required of a medium with a magnetic reversalwidth of 25 nanometers or less on a simple model, reveal that requiredconditions are a medium layer thickness of 15 nanometers or less and amagnetic coercivity of 5 kOe (oersted).

On the other hand, even under the precondition that the magnetic(recording) field generated by the write element in longitudinalrecording has a saturated flux density (hereafter Bs) of 2.4 T (tesla)which is the maximum preferred level usable in a magnetic pole material,the upper figure will still be limited to 9 kOe. In this case, when themagnetic coercivity of the recording layer of the medium exceeds 5 kOe,obtaining a magnetic recording field strong enough to magnetize themedium is difficult. When the magnetic layer thickness of the cobaltalloy magnetic layer is below 15 nanometers, the actual volume ofcrystal grain becomes small so that the magnitude of the thermal energy(in other words, energy agitating the magnetization) can no longer beignored compared to the anisotropic energy (in other words, energy forstabilizing the magnetization in a fixed direction) of the individualparticles. The thermal fluctuation becomes drastic, causing the problemthat thermal decay reduces the magnitude of the record magnetization astime passes. To suppress this thermal decay, the magnetic coercivitymust be further increased or the volume of the crystal grains increased.

However as described above, there is an upper restriction on theallowable magnetic coercivity when the magnetic field of the head islimited. Furthermore, increasing the layer thickness in order toincrease the volume of the crystal grains signifies an increase in themagnetic transition area due to an increase in the demagnetization fieldor in other words, means a drop in the allowable linear recordingdensity.

However, attempting to attain a sufficient volume for the crystal grainslongitudinally, increases the randomness of the magnetizationdistribution within the medium, leading to increased noise in the mediumand preventing a sufficient S/N (signal-to-noise) ratio from beingobtained. Therefore, achieving longitudinal recording in excess of anareal recording density of 100 gigabits per square inch while satisfyingthe conditions for thermal decay, low noise and sufficient recording ispredicted to be basically difficult.

The perpendicular recording has been proposed to resolve these basicproblems. The perpendicular (magnetic) recording is a method formagnetizing the thin-film layer in a direction perpendicular to thelayer surface and its recording principle is basically different fromthe longitudinal recording of the related art. In the perpendicular(magnetic) recording, the particles are magnetized in a antiparallelconfiguration so adjacent magnetized particles are not made to faceeach, and therefore the perpendicular recording is not so affected bydemagnetization fields. Perpendicular recording may therefore allowmaking the magnetic transition states extremely narrow and also make iteasier to boost the linear recording density. Perpendicular recordingcan also be highly resistant to magnetic decay for the same reason,since the requirements for the medium thin-film as not as stringent asthose for longitudinal recording.

As perpendicular magnetic recording is gathering attention as an idealmethod for high density magnetic recording, mediums of variousstructures and materials combined with thin-film magnetic heads havebeen proposed. Perpendicular recording is composed of a method utilizinga single perpendicular magnetic layer; and comprised of a method formingadjacent flux keeper layers of low magnetic coercivity between the disksubstrate and the perpendicular magnetic layer.

Perpendicular recording has the advantage that by utilizing a doublelayer perpendicular magnetic recording medium possessing a flux keeperlayer and combining a single pole type write element (1): capable ofreducing demagnetization field generated in a recording layer (2): amagnetic recording field can be generated having a steep distributioncompared to the ring head utilized in longitudinal recording. Thistechnology is for example disclosed in the non-patent document 1.

Mediums formed for example from a perpendicular magnetic layer of CoCralloy formed on a flux keeper layer made from a soft magnetic layer suchas permalloy or iron based amorphous alloy or fine crystallized alloyare under evaluation. In recent years, so-called granular mediums withfine particles of cobalt magnetic dispersed in SiO2 or superlatticelayers such as Co/Pd or Co/Pt as the recording layer are also underevaluation. To stabilize magnetic domains of keeper layer, laminatedlayers combining with antiferromagnetic materials or magneticmultilayers which is composed of antiferromagnetically coupledferromagnetic layers are for example being utilized.

The type of write element utilized in perpendicular recording with aperpendicular recording medium possessing a flux keeper layer isgenerally called a single-pole write element. This element does not usea structure of two poles facing each other via an extremely thin gap asdoes the so-called ring write element in longitudinal recording.Instead, the single magnetic pole (main pole) 13 as shown in FIG. 1 ischaracterized by a structure protruding towards the medium. To form amagnetic path however, a pole called an auxiliary pole 16 however isformed so as to put the coil 17 between them.

The auxiliary pole 16 forms a magnetic path in the path sequence of mainpole 13, flux keeper layer 19, auxiliary pole 16, yokes 14, 15, and mainpole 13 and is characterized in that recording can be performed withoptimal efficiency. Since the magnetic flux flowing between the mainpole 13 and the keep layer 19 cuts across the recording layer 18, themagnetic flux flow makes a magnetic recording field, and forms a recordbit 20 in the recording layer 18.

The one serious problem unique to perpendicular recording utilizing themutual effects of a single pole write element and magnetic flux keeperlayer is the remanent magnetization of the main pole. This phenomenon isdesignated in non-patent document 2.

In this phenomenon called, “erase-after-write” (or erasing after write)disclosed in this document, the signal on the medium is erased by adirect current magnetic field due to remanent magnetization immediatelyafter recording. The head in an actual magnetic disk drive is constantlymoving above the disk. Therefore when this phenomenon occurs duringoperation, there is the possibility that data and servo informationmight be destroyed over an extremely wide range on the disk.

This phenomenon is a fatal defect in the reliability of the magneticwrite-read system. One method to avoid this phenomenon described inpatent document 1 is optimizing the shape of the yoke. This method couldeliminate the problem of erasure occurring after writing in the yokesection due to remanent magnetization.

However, though there is a relatively high degree of freedom indesigning the dimensions and shape of the yoke section, the pole tipwhich determines the width of the narrow recording track must be madesmall to meet the increased recording density. So it is necessary toemploy a completely different means to suppress the remanentmagnetization in the pole tip. One means is a method known in therelated art utilizing a magnetic multilayer with a thin film (layer) ofless than one micron in the main pole of the thin film magnetic headused for perpendicular recording.

A structure is disclosed in patent document 2 utilizing a magneticmultilayer in the main pole of the thin film magnetic head used forperpendicular recording. Methods are also disclosed in patent document3, patent document 4, patent document 5 for utilizing optimal materialsand layer structures to stabilize the magnetic domain in magneticmultilayers. However, these methods all have the objective ofstabilizing the magnetic layer of a single magnetic domain and areinadequate or inapplicable as a means to prevent the erasure after writethat is brought about by the single magnetic domain that results frommaking the magnetic pole smaller and narrower. The patent document 6also discloses an example of a thin-film magnetic head utilizing amagnetic multilayer comprised of magnetic layers. However, this methodcan also be seen in the ring thin-film magnetic head utilized inlongitudinal recording and was disclosed in technology to fix a magneticdomain for suppressing noise that accompanies changes in the structureof the magnetic domain during read operation. This structure is alsodifferent from the means for suppressing remanent magnetization in thepole tip after recording and is clearly not suitable.

The above disclosures assume as a precondition use of a materialyielding comparatively satisfactory soft magnetic layer characteristicssuch as Ni—Fe, Fe—Ni alloy, and Fe. These disclosures are thereforeunsuitable for high Bs material combinations exceeding 2.2 T such asFe—Co alloy required for narrow tracks in the future.

[Patent document 1]

JP-A No. 291212/2001

[Patent document 2]

JP-A No. 324303/2002

[Patent document 3]

JP-A No. 54320/1993

[Patent document 4]

JP-A No. 195636/1994

[Patent document 5]

JP-A No. 135111/1995

[Patent document 6]

JP-A No. 49008/1991

[Non-patent document 1]

IEEE Transactions on Magnetics, Vol. MAG-20, No. 5, September 1984, pp.675-662, “Perpendicular Magnetic Recording-Evolution and Future”

[Non-patent document 2]

IEEE Transactions on Magnetics, Vol. MAG-32, No. 1, January 1996, pp.97-102, “Challenges in the Practical Implementation of PerpendicularMagnetic Recording”

[Non-patent document 3]

The 198th Meeting of the Electrochemical Society, Meeting Abstracts, No.582

In a perpendicular recording thin film magnetic head for high densityrecording in excess of 100 gigabits per square inch, a strong magneticfield in excess of 10 kOe must be generated from a narrow pole tip of200 nanometers or less in width in order to write bits clearly on amagnetic recording medium with high magnetic coercivity of 5 kOe ormore.

FIG. 2 is a graph showing the magnetic recording field distributiongenerated by a single pole type write element in the center of therecording track and computed by the 3-dimensional finite element method.The pole width was 150 nanometers to attain the required 140 gigabitsper square inch. The four curves are respectively for a saturation fluxdensity (Bs) of 2.4 T, 2.2 T, 2.0 T, and 1.6 T.

These results revealed that a ferromagnetic alloy mainly of Fe—Co with ahigh Bs of 2.2 T or more is required in the pole tip in order togenerate a recording magnetic field in excess of 10 kOe at the writeelement for a narrow track having a high recording density in excess of100 gigabits per square inch.

FIG. 3 is a graph showing results when many perpendicular recording thinfilm magnetic heads manufactured in different recording pole widthsusing high Bs materials of this type were subjected to 100 write-readrepetitions and the degree of erase-after-write then calculated usingthe change in output as an indicator. The vertical axis is the change inoutput expressed in percent of average rated output over the 100read-write cycles. The horizontal axis expresses the magnetic pole widthof each head. The heads differ from one another only in the magneticpole width and the other parameters are all fixed parameters.

As these results clearly show, virtually no erasure-after-write occurredin heads with a magnetic pole width of 200 nanometers or more, yet theextent of erasure-after-write suddenly increased on tracks narrower than200 nanometers. The changes in output of below 10 percent observed onmagnetic pole widths of 200 nanometers or more were confirmed as almostall being due to fluctuations in the sensitivity of the read elementitself.

In the related art, erasure-after-write is thought to be caused by highrecording efficiency from the combination of single pole type writeelement and keeper layer in the medium. In other words, remanentmagnetization is not as likely to occur in independent write elementsbecause demagnetization fields in the pole occur on the surface bearingto the medium. Therefore, the magnetic flux keeper layer in the mediumhere acts to reduce the demagnetization field in the magnetic polehaving the effect that remanent magnetization is likely to occur.

The results in FIG. 2 however clearly show that this problem occurs morefrequently on narrow tracks having a drop in recording efficiency. Theerasure-after-write phenomenon here is therefore a mode different fromthe erasure-after-write disclosed in the reference documents. This isclearly due to a completely different physical phenomenon occurringwithin the write element.

Magnetization of ferromagnetic material can be considered the result ofan aggregate of tiny magnetic momentum called spin. This spin has theconstant effect of aligning the momentum of the vector in one directionby a mutual effect called exchange coupling. The ferromagnetic materialhowever is processed in a limited size, so in order to prevent a vastincrease in magnetostatic energy emitted to outer peripheral sections,the internal sections are separated into small areas known as magneticdomains.

These different magnetic domains need not always be made to face thesame direction, and these domains are placed entirely in a magneticallyclosed structure. The boundaries of this magnetic domain are (magneticdomain) walls of a limited width. The size is determined by themagnetostatic energy versus the exchange coupling energy from adjoiningnon-aligned spins so that though differing by size and shape,ferromagnets widely known as comprised mainly by iron and cobalt have asize on the order of several hundred to some thousands of nanometers.Therefore, when the scale of the magnetic material is down to a fewthousands of nanometers or less, a magnetic domain wall cannot beformed, and the magnet material tends to form into single domain states.

FIG. 4 shows results of the calculated remanent magnetization found bysimulating the magnetic state of the magnetic pole tip. The verticalaxis expresses stray magnetic fields due to remanent magnetization. Thehorizontal axis expresses the magnetic pole width. These results alsoreveal that the remanent magnetic field suddenly increases at polewidths of 200 nanometers and below.

FIGS. 5A and 5B are conceptual views of the magnetic state of themagnetic pole tip found by the above described simulation. The arrow 55in the drawing indicates the direction of magnetization. When themagnetic pole width is as wide as 300 nanometers (FIG. 5A), the magneticstate is in a so-called closed domain structure. However when themagnetic pole width is a narrow 100 nanometers (FIG. 5B), one can seethat the magnetic state is almost entirely a single domain and thereforea large remanent magnetic field is generated.

Examining the actual magnetic state of the write elements with 300 and120 nanometer magnetic pole widths by spin-polarized scanning electronmicroscopy (SEM) shows as expected, that a with a wide pole width of 300nanometers the magnetism is separated into numerous magnetic domainshaving various directions of magnetization. However, in the case of thenarrow pole width of 120 nanometers, the magnetization is almostcompletely in a single domain state. These results allow concluding thatthe sudden increase in erasure-after-write observed in pole widths below200 nanometers is due to the main pole tip preferring to be a singledomain state.

In magnetic poles of this small size, remanent magnetization is easilyprone to occur because of the tendency for uniform magnetization so thatmany cases of erasure-after-write have a high probability of occurringduring device operation. In addition, in high Bs material such as Fe—Coalloy, the soft magnetic properties are generally inferior to those oftypical soft magnetic materials such as Ni₈₀Fe₂₀. In other words, largehysteresis often appears in the magnetic curve due to the dispersion ofcrystalline magnetic anisotropy as well as materials having a large,positive magnetorestriction coefficient that are factors in inducingremanent magnetization and therefore erasure-after-write. This signifiesthat remanent magnetization is large when the hysteresis of the softmagnetic material is large and when there is no excitation. In thin filmmagnetic heads on the other hand, materials with a positivemagnetorestriction coefficient are known to possess magnetic anisotropyinduced in a direction perpendicular to the surface of the medium by aneffect from anisotropic stress (generally called theinverse-magnetorestriction effect). (See the example in non-patentdocument 3.)

Magnetization is easily faced in a long-axis direction (shape magneticanistrophy) due to the long, narrow shape of the four-cornered cylinderwhich is the original shape of the main pole tip. In addition, thecrystalline magnetic anisotropy also becomes stronger in a directionperpendicular to the surface of the medium because of theinverse-magnetostriction. Therefore along with the single domain statethat was previously described, the problem of erasure-after-write easilytends to occur due to remanent magnetization of the magnetic pole tip.

A structure is therefore required that essentially applies no straymagnetic field to the magnetic recording medium even remanentmagnetization is generated perpendicular to the surface of the medium.

The inventors perceived that remanent magnetization can be suppressed ina thin film perpendicular magnetic recording head by employing a closeddomain structure for the magnetic material even in magnetic poles ofextremely small size by utilizing a magnetic multilayer structure and anoptimal combination of materials capable of effectively eliminating themutual exchange effect within the magnetic material causing a singledomain state.

SUMMARY OF THE INVENTION

In other words, to resolve the aforementioned problems of the relatedart, the thin film perpendicular magnetic recording head and magneticdisk drive of the present invention are comprised of a main pole, areturn path for supplying a magnetic flux to the main pole, and aconductive coil for excitation of the main pole and the return path,wherein the main pole has a width of 200 nanometers or less, and thatmain pole possesses a magnetic multilayer made up of a high saturationflux density layer and low saturation flux density layer, the highsaturation flux density layer contains an iron-cobalt alloy, and thedirection of magnetism of a pair of the high saturation flux densitylayers facing each other by way of the low saturation flux density layeris an antiparallel array in the magnetic multilayer. It should be notedhere that the low saturation flux density material here may comprise anon-magnetic material.

The main pole possesses a magnetic multilayer made up of a highsaturation flux density layer and low saturation flux density layer and,the thickness of the low saturation flux density layer is within a rangeof 0.5 nanometers or more to 5 nanometers or less, and the highsaturation flux density layer preferably has a thickness from 10nanometers or more to 50 nanometers or less.

The present invention can provide a thin film perpendicular magneticrecording head and magnetic disk drive capable of preventing erasureafter write since a main pole comprised of magnetic multilayer withclosed domain structures is utilized to suppress remanent magnetization.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view expressing a typical structure of theperpendicular recording method and in particular the magnetic recordingmedium containing the flux keeper layer and thin-film magnetic head andpositions of the recorded bits;

FIG. 2 is a graph showing the dependence of the thin film magnetic headmagnetic recording field distribution on the main magnetic pole materialBs;

FIG. 3 is a graph showing the rate of change in output versus the writepole width;

FIG. 4 shows the relation of remanent magnetization to magnetic polewidth;

FIG. 5A is a diagram showing the magnetic state of the magnetic pole tipwhen the pole width is 300 nanometers;

FIG. 5B is a diagram showing the magnetic state of the magnetic pole tipwhen the pole width is 100 nanometers;

FIG. 6 is a drawing showing the layers of the pole tip section of thethin film magnetic recording head of the first embodiment of the presentinvention;

FIG. 7 is a phase diagram of the Bs of the 3-element alloy of cobalt,nickel and iron;

FIG. 8 is a perspective view showing the overall structure of the writeelement of the first embodiment of the present invention;

FIG. 9A is a drawing showing the relation of the layer structure of thepole tip and the remanent magnetic field;

FIG. 9B is a graph showing the relation of the layer structure of thepole tip and the remanent magnetic field;

FIG. 10A is a graph showing the relation of the layer structure of thepole tip and the change in output;

FIG. 10B is a graph showing the relation of the layer structure of thepole tip and the change in output rate and the overwrite;

FIGS. 11A-11D are graphs showing the relative frequency distribution ofthe change in output for groups of thin-film magnetic heads withdifferent pole tip layer structures;

FIG. 12 is a characteristics chart showing the relation of the thicknessof the low saturation flux density layer and the overwrite;

FIG. 13 is concept diagram of the magnetic disk device of the presentinvention;

FIG. 14A is a cross sectional view of the magnetic recording mediumcontaining an improved flux keeper layer utilized in the firstembodiment of the present invention;

FIG. 14B is a cross sectional view of the magnetic recording mediumcontaining an improved flux keeper layer utilized in the firstembodiment of the present invention;

FIG. 15 is a cross sectional view of the pole tip of the secondembodiment of the present invention;

FIG. 16 is a cross sectional view of the pole tip of the thirdembodiment of the present invention;

FIG. 17 is a perspective view of the write element of the fourthembodiment of the present invention;

FIG. 18 is a cross sectional view of the thin film recording head of thefifth embodiment of the present invention;

FIG. 19 is a cross sectional view of the thin film recording head of thesixth embodiment of the present invention;

FIG. 20A is a data characteristics graph rating the stability of record(write) operation (when overshoot is 130%) of the seventh embodiment;

FIG. 20B is a data characteristics graph rating the stability of record(write) operation (when overshoot is 79%) of the seventh embodiment;

FIG. 21 is a graph illustrating the overshoot;

FIG. 22 is a data characteristics graph showing the relation of theovershoot value and the signal fluctuation width of the seventhembodiment;

FIG. 23 is a data characteristics graph showing the relation of theovershoot for nonlinear bit shift in the seventh embodiment;

DETAILED DESCRIPTION OF THE INVENTION

The thin film perpendicular magnetic recording head of the presentinvention is composed of a main pole, a return path for supplying amagnetic flux to said pole, and a conductive coil for excitation of themain pole and the return path. The main pole is also characterized inhaving a width of 200 nanometers or less; possessing a magneticmultilayer made up of a high saturation flux density layer (high Bslayer) and a low saturation flux density layer (low Bs layer); and thehigh saturation flux density layer contains an iron-cobalt alloy.

The low saturation flux density layer also has a thickness within arange of 0.5 nanometers or more to 5 nanometers or less. In the magneticmultilayer, the direction of magnetism is in an antiparallel array inthe pair of high saturation flux density layers facing each other by wayof the low saturation flux density layer.

The high Bs layer is preferably made up of four or more layers and astructure with high Bs layers of different thickness is more effective.A full effect can be obtained if the number of high Bs layers is tenlayers or more.

Adding an additive elements of 10 percent or less in the high Bs layer,allows using a ferromagnetic material having improved soft magneticproperties. If this high Bs layer at this time has a body-centered cubicstructure, both a high Bs of 2.2 T or more and even more satisfactorysoft magnetic properties can be obtained.

In the magnetic multilayer made from a high Bs layer and low Bs layer,the layers are arrayed in parallel in a direction perpendicular to themedium surface facing the main pole.

In terms of obtaining soft magnetic properties, the non-magnetic layerand low Bs layer are preferably below 2.2 T, and have a face centeredcubic structure as the crystalline structure.

A material of Ni—Cr, Ni—Fe, Ni—Fe—Cr, Ta, will prove satisfactory.

Since the main magnetic pole must generate a high magnetic recordingfield capable of sufficiently magnetizing a magnetic recording medium ofhigh magnetic coercivity, a preferred magnetic multilayer layerthickness is a low Bs layer or non-magnetic layer of 5 nanometers orless, or a high Bs layer of 50 nanometers or less, or is a combinationof both layers. A more complete effect can be obtained if the high Bslayer is 20 nanometers or less.

An ideal means for forming a main pole comprised of a magneticmultilayer is a method combining a deposition process using sputteringand an etching process using ion milling.

The write element return path can achieve stable recording operationwith optimal efficiency by utilizing a single Bs layer comprised ofsmall material less than 2.2 T, or a multilayer of soft magneticmaterial.

By utilizing the above structures singly or in multiple combinations, ahigh reliability perpendicular thin film magnetic recording headgenerating virtually no remanent magnetization can be supplied at a lowcost.

Further, by combining this type of thin film magnetic head with amagnetic recording medium comprising a flux keeper layer, ahigh-capacity, yet low cost magnetic disk drive can be achieved. In thiscase, the effect is rendered that a multilayer structure with fluxkeeper layer and a write element main pole with suppressed remanentmagnetization are obtained so that the drive reliability is furtherenhanced.

Many attempts to further improve recording density have been attemptedin recent years by purposely applying longitudinal components to themagnetic recording field and magnetic anisotropy of the medium recordinglayer have been made. However, since perpendicular components aredominant in comparison with longitudinal components in the magneticrecording field, this kind of method is also usually grouped under theperpendicular recording. Also, methods to add longitudinal magneticcomponents to the recording field by contriving means such as auxiliarypoles or write elements whose structure includes an improved recordingfield gradient are being evaluated. However these methods are nodifferent from the basic function of magnetizing the medium using themagnetic field output from the medium surface that faces the main poleso that these methods may also be referred to as perpendicular thin filmmagnetic recording heads. The present method is also applicable andeffective on these magnetic recording systems or write elements.

The perpendicular thin film magnetic recording head and magnetic diskdrive of the present invention is hereafter described in detail whilereferring to the accompanying drawings.

The magnetic multilayer (magnetic multilayer film) comprising the mainpole of the present invention is formed by radio-frequency magnetronsputtering device as described next. The material for forming themagnetic pole is sequentially deposited on the base formed beforehandfor forming the ceramic substrate in an argon gas chamber at a pressureof one to six milli-Torr. Here, Fe—Co, Ni—Cr, Ni—Fe—Cr, Ta, Al, Al—O,Si, Si—O were utilized as the sputtering target. Radio frequency poweris applied to cathodes positioned on the targets to generate a plasmawithin the apparatus. Layers are then formed in sequence by opening andclosing one at a time, a shutter positioned at each cathode, and themultilayer formed.

During forming of the layer, a permanent magnet is utilized to apply amagnetic field parallel to the surface of the substrate, for applyinguniaxial magnetic anisotropy. Patterning for forming elements on thesubstrate is performed by a series of processes including exposing anddeveloping the photoresist. And the process also includes ion-milling.Finally, the substrate is machined in a slider and by combining with astainless suspension is mounted in the magnetic disk drive.

First Embodiment

FIG. 6 is a cross sectional view showing the structure of the magneticmultilayer of the first embodiment of the present invention. A high Bslayer 63 and a nonmagnetic layer 64 are alternately deposited on thesubstrate 61 by way of the underlayer 62, and finally covered by aprotective layer 65. This high Bs layer 63 is Fe₇₀Co₃₀ having abody-centered cubic structure. The underlayer 62 and nonmagnetic layer64 are both Ni₈₀Cr₂₀ (film thickness 3 nanometers) having aface-centered cubic structure. FIG. 6 shows the magnetic multilayer asseen from the medium surface facing the main pole.

The thickness of each high Bs 63 layer is calculated for a total high Bslayer thickness of 200 nanometers so each layer in the example in FIG. 6is 25 nanometers. The low Bs layer is nickel-chromium alloy and is 3nanometers thick. Measuring the magnetization curves showed that themagnetic coercivity along the easy axis and the hard axis were bothbelow 4 Oe, the anisotropic magnetic field Hk was 10 Oe or less, themagnetostriction coefficiency was a large, positive value of +5×10⁻⁶.The high Bs layer 63 had a Bs value of 2.4 T, matching the Bs predictedfrom phase diagram of the Fe—Co—Ni 3 element alloy as shown in FIG. 7.

In all of the following embodiments including the present embodiment,the Bs of the high Bs layer is 2.2 T or more. Therefore, in the case ofthe Fe—Co—Ni alloy, the composition utilized for section 71 enclosed bythe boundary 2.2 T in the phase diagram of FIG. 7 may be used. In thecase of the composition expressed by (Fe_(α)Co_(β))_(100-γ)M_(γ) (where,M is B, Ti, Nb, Al, Al—O, Si, Si—O; and 0≦r≦15), the Bs for a 3-elementalloy also containing an additive M is 2.2 T or more so that thepreferable composition corresponds to the section where (Fe_(α)Co_(β))is surrounded by the boundary for 2.4 T in FIG. 7.

The example in FIG. 6 showed the high Bs layer having four layershowever the inventors here manufactured the head varying it from 1 to 25layers.

The thin film magnetic head shown in FIG. 8 is formed from thesemagnetic multilayers by undergoing wafer processes and slider machiningprocesses including a: (1) resist coating-baking process, (2) lightexposure process, (3) developing process and (4) ion milling process.Here, the pole width was made 150 nanometers in the surface of the pole13 facing the medium, however absolutely identical results can beobtained with a pole width of 200 nanometers or less. The ferromagneticmaterial for the yoke 14, the return path 15, and the auxiliary pole 16was in all cases nickel-iron (Ni—Fe) alloy, however the Bs was 1 T orless since nickel made up more than 80 percent of the component. Themagnetostriction coefficient appeared as a negative value. By utilizinga negative magnetorestriction material in this way, the aforementionedinverse magnetorestriction effect ensures that the magnetism of the yoke14, the return path 15, and the auxiliary pole 16 will tend to be stablein a direction parallel to the surface of the medium. This materialallows avoiding problems such as remanent magnetic fields and unstablecharacteristics in magnetization of sections other than the pole tip.

The read element is omitted here, however it is included in all of thefollowing embodiments and can be applied to read elements of all typesof principles and structures including Current-in-Plane-GiantMagnetoresistive (CIP-GMR) elements, Current-Perpendicular-GiantMagnetoresistive (CIP-GMR) elements, Tunnel Magneto-resistive (TMR orMJT) or Magneto Tunnel Junction (MTJ) elements, etc.

FIG. 9A is a drawing showing results from calculations for finding theideal layer structure prior to fabricating the head. As describedpreviously, the magnetostriction coefficient is a positive value in highBs material exceeding 2.2 T so that magnetization tends to easily facethe medium surface due to the inverse magnetorestriction effect.Therefore in designing the layer structure, the remanent field 92 mustbe made sufficiently low even if the magnetization 91 of each high Bslayer 63 is facing the medium surface.

The advantage when using a multilayer is that the magnetization 91 ofeach high Bs layer is in an anti-parallel configuration as shown in FIG.9A. The remanent field 92 is therefore not applied to the medium becauseof the return flow on the magnetic pole itself. FIG. 9B shows thecalculated results of the dependence of remanent magnetization on thenumber of high Bs layers assuming this anti-parallel configuration. Asshown in the figure, at least four or more layers are required in viewof the need to this remanent field smaller than the magnetic coercivityof the medium.

FIG. 10 shows results from evaluating characteristics of theperpendicular recording head manufactured in this way. FIG. 10A is agraph showing the dependence of the change in output upon the layerstructure. FIG. 10B is a graph showing the dependence of the overwriteon the layer structure. These figures clearly show that the change inoutput is greatly improved by using four layers or more. Further, at tenlayers or more, the change in output rate becomes fixed at 10 percent orless. As related before, the sensitivity of the read element itselffluctuates at output changes of 10 percent or less soerasure-after-write can be completely suppressed at 10 layers or more.

FIG. 11 showed the relative frequency distribution of the change inoutput for groups of thin-film magnetic heads. All the heads candefinitely be confirmed as having a change in output of 10 percent orless when using 10 layers. A look at FIG. 10B on the other hand, showsthat the overwrite erasure has started to deteriorate at 20 layers ormore and at 25 layers has fallen below 30 dB which is generallyconsidered a required level. This deterioration is due to the largeincrease in volume taken up by nonmagnetic layers when too many layershave been added, and may lead to a drop in the magnetic recording field.

Results from the embodiment showed that four or more layers are requirefor high Bs material and that a full effect can be obtained at 10 layersor more. This is equivalent to a thickness of 50 nanometers or less forhigh Bs layers and preferably within 20 nanometers or less. On the otherhand, 20 layers or less or at a film thickness of 10 nanometers or lessis required for recording (write) performance.

The nonmagnetic layer 64 and the underlayer 62 that serve to divide thehigh Bs layers should be at least within 2.2 T and smaller than the Bsof the high Bs layer and preferably should be a material of 2.0 T withsmall crystalline magnetic anisotropy. Here, nickel-chromium (Ni—Cr)alloy is generally utilized for non-magnetic characteristics at roomtemperature, however if the crystalline structure is a face centeredcubic structure then the same results can be obtained even when low Bsmaterials with magnetic elements such as nickel-iron, or non-magneticmaterials such as Ni—Fe—Cr are included. The same satisfactory effectscan be obtained when selected from the above group of materials, whetherthe underlayer 62 and intermediate layer 64 are made from the samematerials or made from different materials.

Evaluations were made of different types of structures for low Bs layerthickness. It was found that an 0.5 nanometer thickness is necessary toprevent ferromagnetic coupling (generally called the orange peel effect)between high Bs layers. In regards to the upper limit, FIG. 12 showsresults of actual measurements of overwrite when the low Bs 64 layerthickness was changed in a range from 0.5 nanometers to 10 nanometers.These results reveal that the recording (write) characteristicsdeteriorate greatly when the thickness of low Bs layer 64 exceeds 5nanometers. This deterioration occurs because the percentage of volumetaken up by the low Bs layer has increased creating the same effectessentially as if the overall Bs level had dropped, and so the magneticrecording field weakens.

FIG. 13 is a concept view of magnetic disk drive comprising the headmanufactured in the first embodiment and the magnetic recording mediumhaving the flux keeper layer. The slider 121 holding the thin filmmagnetic head is supported by the suspension arm 122. Information isread at the desired location positioned on the disk 124 by thepositioner device 123, and rotation of the disk 124 is controlled by thespindle motor 125. A signal (servo signal) showing the position isrecorded on the disk 124 beforehand. After processing the servo signalread by the head on the mechanism control circuit 129, closed loopcontrol is implemented by feedback to the positioner device 123.

User data entering by way of the external interface 126 is encoded,processed and converted into a recording current waveform by asatisfactory method for the magnetic recording system in the dataencoding/recording system 127, and the bits are written on the medium byexcitation of the write element. Conversely, stray magnetic fields fromwritten bits are converted into electronic signal by sensing them with aread element and after being waveform-shaped and decoded in the datareproducing/decoding system 128 by a satisfactory method for themagnetic recording system are recreated as user data. Therefore, as aresult of using the thin magnetic head of the present invention in amagnetic disk drive operating in this way, stable operation can beachieved without causing problems such as erase-after-write. Ahigh-capacity and highly reliable, yet low cost magnetic disk drive canin this way be achieved.

With the distance between the layer center thickness set as D, and thegap between the main pole tip and the flux keeper layer of medium duringdevice operation as H, if the flux between the high Bs layers of themain pole in a remanent state is set as D≦2×H to allow an effectivereturn flow, then it is known that the long term reliability inparticular will be excellent.

In the magnetic recording medium with flux keeper layer used up untilnow, the flux keeper layer structure was made from a singleferromagnetic layer. However, a magnetic disk drive combining a magneticrecording media with a flux keeper layer made from a multilayerstructure, and thin film magnetic head of the present invention willprove effective in achieving a magnetic disk drive with more stableoperation and high reliability.

FIG. 14A and FIG. 14B are cross sectional views of the structure of theimproved flux keeper layer. FIG. 14A is a magnetic recording mediumcomprised of a ferromagnetic layer 132 divided by a non-magneticmaterial layer 133 in the flux keeper layer 19 formed on a substrate130. By combining the magnetic recording medium configured as described,with the thin film magnetic head of this embodiment, a main polecomprised of merely six high Bs layers can completely suppresserasure-after-write. It was also clear that the magnetic disk mountedwith this head can deliver stable operation. Further, by selecting analloy material containing mainly any of Ru, Cr, Ir, Rh as thenonmagnetic layer 133, an antiferromagnetic exchange can occur betweenthe ferromagnetic layers 132, and the stability of the magnetic statewithin the flux keeper layer can be improved so that erasure-after-writecan be completely suppressed even when there are only a few (6) high Bslayers in the main pole.

Next, FIG. 14B is a layer structure equivalent to that of FIG. 14A, butinserted with an antiferromagnetic layer 135. A satisfactory effect wasobtained when IrMn, FeMn, PtMn, CrMnPt, NiO were selected as theantiferromagnetic layer. Both FIG. 14A and FIG. 14B employed a doublelayer structure for the ferromagnetic layers 132, however the samesatisfactory effect was obtained even when three to five ferromagneticlayers 132 were used. The beneficial effect in the multilayer keeperlayer was drastically increased when the thickness of the ferromagneticlayers 132 were 100 nanometers or less.

Accordingly, by combining a magnetic recording medium having an improvedflux keeper layer, with a thin film magnetic head of the presentinvention, a magnetic disk drive of excellent reliability can beachieved.

Second Embodiment

In the first embodiment, the layers were formed to the same thicknesswithin a certain range (generally about ±5%) for variations duringforming of the high Bs layer for the main pole. However, by purposelyforming a structure of different thickness, even further improvementscan be achieved.

FIG. 15 is a cross sectional view showing the structure of this type ofembodiment. Here, a film thickness difference of 20 percent was madebetween a first high Bs layer (odd numbered high Bs layer from thesubstrate side) 63 and a second high Bs layer (even numbered high Bslayers from the substrate side) 63′ and these layers then alternatelyformed in a laminated structure. By utilizing this structure, anidentical magnetic state can be constantly achieved for eachmagnetostatic exchange by high Bs layers in a remanent magnet state.Consequently, the same characteristics appear for 10¹⁰ cycles of writeoperations which is an extremely large number, showing that the stableoperation of the magnetic disk device has been improved.

Third Embodiment

An example of the second embodiment with high Bs layers of the main polehaving different structures for each layer is shown in FIG. 16. Thisembodiment has a structure where among the high Bs layers, the high Bslayer nearest the substrate and the high Bs layer farthest from thesubstrate are made thinner than the other high Bs layers. In thisstructure, since these two layers have only a high Bs layer on one side,the weak remanent magnetic fields are not applied to the media. It wasalso found that satisfactory read/write characteristics can be obtainedwith no loss in long term stability of bits written on the magneticrecord medium.

The structure of the write element used in all of the embodiments up tonow is shown in FIG. 8. The following embodiments of the presentinvention are for a thin film magnetic head other than the structureshown in FIG. 8.

Fourth Embodiment

FIG. 17 is a perspective view of the write element in which the mainpole tip 13 is connected directly to the return path 15 but with theyoke 14 of FIG. 8 omitted. All the layer structure combinations of theabove first through third embodiments were tried and absolutely the sameresults were obtained. The process for forming the write element wasgreatly shortened in this embodiment so a thin film magnetic head withhigh reliability, high performance can be achieved at a lower cost.

Fifth Embodiment

FIG. 18 is a cross sectional view of the thin film magnetic head of thepresent invention. In this structure, the main pole taper section 179 iscontacting the main pole tip 13 and layer surface. As it nears thesurface 177 facing the medium, the main pole taper section 179 becomesnarrower in size in the direction of layer thickness, forming into awedge shape. A material for the ferromagnetic alloy comprised mainly ofCo—Ni—Fe or Fe—Ni is utilized having a Bs higher than the yoke 14 andlower than the main pole tip 13.

A structure of this type may provide an approximately 30 percentincrease in the magnetic recording field. Though the magnetic coercivityof the recording layer exceeded 6 kOe in the magnetic recording medium,and a high overwrite of more than 35 dB was obtained. The arealrecording density was therefore improved approximately 30 percent evenwith the same magnetic pole width.

The yoke 14 is in contact with the substrate side surface of this mainpole taper section 179. However, by forming the main pole tip and themain pole taper section 179 more to the substrate side from the yoke 14,it was clearly found that absolutely the same effects are obtained evenin a structure where the yoke 14 and main pole tip 13 are in directcontact.

Sixth Embodiment

FIG. 19 is a cross sectional view of the thin film magnetic head of thepresent invention. The main pole tip 13 is positioned more to thesubstrate side than the auxiliary pole 16. The auxiliary pole tip 181extends from the auxiliary pole 16 towards the main pole tip 13 on thesubstrate side 177. This auxiliary pole tip 181 will cause a steepergradient on the trailing side (side opposite the substrate) of themagnetic field generated from the main pole tip 13. Utilizing thisstructure improved the signal resolution by 15 percent. The signalresolution is thought to be dependent on this magnetic recording fieldgradient. A stable and highly reliable, thin film magnetic head witheven higher record (write) density can therefore be provided.

Incidentally, even supposing use of a structure of FIG. 19 with theauxiliary pole tip 181 removed, the effect of the invention is in nowway diminished in terms of at least the stability and reliability.

Seventh Embodiment

FIGS. 20A and 20B are data characteristics graphs rating the stabilityof write operation in a magnetic disk drive mounted with the single poletype thin film magnetic head with multilayer main pole of the presentinvention.

FIG. 20A shows the case when set to a write current overshoot of 130percent. FIG. 20B shows the case when set to a write current overshootof 70 percent. The overshoot referred to here is an indicator shown for(lp−ln)/ln×100 utilizing the electrical current value ln of the flatsection and the peak current lp shown along with the write waveform inFIG. 21.

When the overshoot is set to a large value as shown in (A), there arelarge fluctuations in the write (record) level regardless of whether amultilayer pole is used and erase-after-write occurs often. However,when the overshoot is set to a small value as shown in (B), then it canbe seen that erase-after-write does not occur at all.

The overshoot value is generally set in the circuit 127 of the magneticdisk device. However since overshoot is an indicator strongly related towrite performance at high frequencies, not only the head, but also themedium characteristics (properties) and functions of the drive overallmust ultimately be decided. To establish these, an overshoot value witha wide a range as allowable in the thin film magnetic head of thepresent invention is essential for attaining reliability and performancein the magnetic disk drive.

FIG. 22 is a graph showing the changes in output width when theovershoot values were changed. As described above, the change in outputwidth expresses the extent of erase-after-write. An example of asingle-layer pole used in the thin film magnetic head is also shown atthe same time for reference. As can be understood from this graph, alarge erase-after-write is constantly occurring in the single layer ofthe present embodiment except for the times when there is an extremelysmall overshoot. However, it can be seen that in the multilayer pole ofthe present invention, erase-after-write is effectively suppressedwithin a range of 100 percent. Next, FIG. 23 is a data characteristicsgraph showing the relation of nonlinear bit shift to overshoot as animportant indicator for showing overall performance of the magneticrecording system and therefore the magnetic disk drive.

It can be seen that an overshoot of 50 percent or more is requiredregardless of whether the pole is a single layer or multilayer. Thethreshold of 50 percent in this case is largely determined by theperformance of the medium and record (write) current transfer pathcharacteristics. Clearly however, it is effective at least in thepresent invention for achieving both suppression of erase-after-writeand suppression of non-linear bit shift.

In the present embodiment, the overshoot which is an essential elementfor determining magnetic disk drive performance is strongly related tostable write operation, and the invention is indispensable for achievingboth drive performance and reliability. Different changes (number oflayers, material, layer thickness, etc.) and variations in the structureof the magnetic pole may be utilized and can achieve almost the sameeffect as the invention if within the scope and coverage of the presentinvention.

The present invention is capable of suppressing erasure-after-writewhile maintaining a sufficiently large magnetic recording field even onnarrow tracks of 200 nanometers or less by utilizing a magnetic polewidth for high recording densities exceeding 100 gigabits per squareinch, and is further capable of supplying a high performance and highreliability perpendicular thin film magnetic recording head at a lowcost. Further, a high reliability magnetic disk drive can be achieved bycombining this type of thin film perpendicular magnetic head of thepresent invention with a magnetic recording medium comprising a fluxkeeper layer.

1. A magnetic disk drive including a magnetic recording medium, aperpendicular magnetic recording head, and a positioning device forpositioning the perpendicular magnetic recording head over the magneticrecording medium, said magnetic disk drive supplying write electricalcurrent to the perpendicular magnetic recording head, said perpendicularmagnetic recording head comprising: a main pole including a magneticmultilayer composed of a high saturation flux density layer and a lowsaturation flux density layer; a return path for supplying a magneticflux to the main pole; and a conductive coil for excitation of thereturn path, wherein: the high saturation flux density layer contains anFe—Co alloy, the width of the main pole is 200 nanometers or less, thedirection of magnetization in a pair of the high saturation flux densitylayers of the magnetic multilayer facing each other with respect to thelow saturation flux density layer is oriented in an antiparallelarrangement by magnetostatic coupling between magnetization of the highsaturation flux density layers, and the number of turns of the coil of awrite element is less than or equal to
 4. 2. A magnetic disk driveincluding a magnetic recording medium, a perpendicular magneticrecording head, and a positioning device for positioning theperpendicular magnetic recording head over the magnetic recordingmedium, said magnetic disk drive supplying write electrical current tothe perpendicular magnetic recording head, said perpendicular magneticrecording head comprising: a main pole including a magnetic multilayercomposed of a high saturation flux density layer and a low saturationflux density layer; a return path for supplying a magnetic flux to themain pole; and a conductive coil for excitation of the return path,wherein: the width of the main pole is 200 nanometers or less, thethickness of the low saturation flux density layer is within a range of0.5 nanometer to 5.0 nanometers, the thickness of the high saturationflux density layer is within a range of 10 nanometer to 50 nanometers,the direction of magnetization in a pair of the high saturation fluxdensity layers of the magnetic multilayer facing each other with respectto the low saturation flux density layer is oriented in an antiparallelarrangement by magnetostatic coupling between magnetization of the highsaturation flux density layers, and the number of turns of the coil of awrite element is less than or equal to
 4. 3. The magnetic disk driveaccording to claim 1, wherein said main pole is arranged at the trailingside of the return path, and said perpendicular magnetic recording headfurther comprises: a yoke arranged between the main pole and the returnpath; and a main pole taper section arranged between the yoke and themain pole, wherein the number of turns of the coil of the write elementis greater than or equal to
 3. 4. The magnetic disk drive according toclaim 2, wherein said main pole is arranged at the trailing side of thereturn path, and said perpendicular magnetic recording head furthercomprises: a yoke arranged between the main pole and the return path;and a main pole taper section arranged between the yoke and the mainpole, wherein the number of turns of the coil of the write element isgreater than or equal to
 3. 5. A magnetic disk drive including amagnetic recording medium, a thin film perpendicular magnetic recordinghead, a positioning device for positioning the thin film perpendicularmagnetic recording head over the magnetic recording medium, and a devicecontrol portion for supplying a write electrical current to the thinfilm perpendicular magnetic recording head and encoding write data, saidthin film perpendicular magnetic recording head comprising: a main poleincluding a magnetic multilayer composed of a high saturation fluxdensity layer and a low saturation flux density layer; an auxiliarypole; a return path for supplying a magnetic flux to the main pole; anda conductive coil for excitation of the main pole and the return path,wherein: the width of the main pole is 200 nanometers or less, thethickness of the low saturation flux density layer is within a range of0.5 nanometers to 5.0 nanometers, the thickness of the high saturationflux density layer is within a range of 10 nanometers to 50 nanometers,and overshoot of the write electrical current is controlled less orequal to 100% by the device control portion.
 6. A magnetic disk driveaccording to claim 5, wherein the overshoot of the write electricalcurrent is controlled within a range of 50% to 100% by the devicecontrol portion.
 7. A magnetic disk drive according to claim 5, whereinthe magnetic recording medium comprises: a recording layer comprising aferromagnetic material with high coercivity and which retains writtendata through its uniaxial magnetic anisotropy; and a flux keeper layerwith low coercivity and which contributes to the generation of amagnetic recording field through interaction with a write element.
 8. Amagnetic disk drive including a magnetic recording medium, a thin filmperpendicular magnetic recording head, a positioning device forpositioning the thin film perpendicular magnetic recording head over themagnetic recording medium, and a device control portion for supplying awrite electrical current to the thin film perpendicular magneticrecording head and encoding write data, said thin film perpendicularmagnetic recording head comprising: a main pole including a magneticmultilayer composed of a high saturation flux density layer and a lowsaturation flux density layer; an auxiliary pole; a return path forsupplying a magnetic flux to the main pole; and a conductive coil forexcitation of the main pole and the return path, wherein: the width ofthe main pole is 200 nanometers or less, the high saturation fluxdensity layer contains an Fe—Co alloy, the direction of magnetization ina pair of the high saturation flux density layers of the magneticmultilayer facing each other by way of the low saturation flux densitylayer is oriented in an antiparallel arrangement, and overshoot of thewrite electrical current is controlled less or equal to 100% by thedevice control portion.
 9. A magnetic disk drive according to claim 8,wherein the overshoot of the write electrical current is controlledwithin a range of 50% to 100% by the device control portion.
 10. Themagnetic disk drive according to claim 8, wherein the magnetic recordingmedium comprises: a recording layer comprising a ferromagnetic materialwith high coercivity and which retains written data through its uniaxialmagnetic anisotropy; and a flux keeper layer with low coercivity andwhich contributes to the generation of a magnetic recording fieldthrough interaction with a write element.